Sorry guys. I will try to clarify and it may be that I'm talking about two different situations.
Typically I think the question is asked like this: Who have you trained under?
Although I have been in Instructor A's dojo, I really worked with Instructor B but instructor A has tested me and signed my certs.
The other situation is more delicate: You trained at a dojo where you and the instructor are very close in expertise although they hold higher rank than you.
What is the criteria for recognizing someone as your teacher in the formal sense? Maybe you both see the situation differently. In my case, I may be totally off base for not recognizing someone as my teacher and would want to correct that. Where do you draw the line between teacher and training partner or teacher and chief instructor of the dojo? I've been to seminars taught by Yamada Sensei but I would not consider him my teacher. Suppose I attended 10 Yamada seminars a year, does that change things???
Hope that helps.